Various processes have been known heretofore for production of an aromatic nitrile compound from a raw material compound which is an aromatic hydroxymethyl compound, an aromatic alkoxymethyl compound or an aromatic aldehyde compound.
There are known, for example, processes which comprise reacting an aromatic hetero-cyclic aldehyde [e.g. furfural (2-furylaldehyde), 2-thienylaldehyde or 3-pyridylaldehyde] or an aromatic aldehyde (e.g. benzaldehyde) with a hydroxyamine salt to form an oxime and then dehydrating the oxime to produce a corresponding nitrile (e.g. furonitrile) [see Synthetic Communications, Vol. 30, pp. 3109-3114 (2000); Synthesis, pp. 190-191 (1982); Synthesis, pp. 243-246 (2003); Synthetic Communications, Vol. 13 No. 12, pp. 999-1006 (1983)].
These processes, however, comprise two steps of oxime formation and subsequent dehydration; require a dehydrating reagent (e.g. phtalic anhydride or methanesulfonyl chloride) of ordinarily at least one equivalent; when hydroxyamine sulfate is used, it is difficult in some cases to separate the formed aromatic nitrite compound from an inorganic sulfate.
There is also known a process which comprises reacting an aromatic aldehyde with ammonia gas in a gas phase in the presence of a catalyst consisting of copper and a solid acid, to produce an aromatic nitrile compound (JP-A-2000-239247). In this process, however, catalyst preparation need be conducted at a high temperature of 500° C. and excessive ammonia of 2.7 to 10.3 equivalents is required, which is disadvantageous industrially; moreover, a special facility is required for a gas phase reaction at high temperatures of 280 to 330° C.; furthermore, the raw material aldehyde compound is not usable when it is thermally unstable or has a high boiling point, which is a drawback.
There is also known a process for converting an aromatic aldehyde into a corresponding aromatic nitrile compound, using sodium azide in the presence of aluminum chloride [Synthesis, Vol. 7, pp. 641-642 (1992)]. However, use of highly toxic sodium azide in 6 equivalents and aluminum chloride in 2 equivalents is not preferred in industrial practice of the process, from the standpoint of safe operation.
There is further known a process using either of an aromatic aldehyde and benzyl alcohol, and aqueous ammonia and potassium peroxodisulfate in the presence of a nickel catalyst [Chemistry Letters, Vol. 4, pp. 571-574 (1990)]. In this process, however, there are problems that a large excess of ammonia (10 equivalents) is required and, moreover, a benzoic acid compound corresponding to the raw material used is formed as a by-product in an amount of 10 to 20%.
Thus, in the technical field to which the present invention belongs, it has been desired to solve the drawbacks of the prior art and develop a process which can produce an aromatic nitrile compound easily under mild conditions without using a special reaction apparatus or a special reaction reagent.
In view of such a situation, the present inventor made a study on a process which can produce an aromatic nitrile compound from either of an aromatic hydroxymethyl compound, an aromatic alkoxymethyl compound and an aromatic aldehyde compound, or from a mixture thereof. As a result, the present inventor found unexpectedly that the above aim could be solved by reacting the above aromatic compound with an oxidized bromine compound in the presence of an acid catalyst, using ammonia or the like as a nitrogen source. The present invention has been completed based on this finding.